1. Field of the Invention
The present invention generally relates to helmet-mounted night vision enhancement systems and more specifically, to an image intensifier subsystem arrangements for helmet-mounted night vision enhancement systems.
2. Description of Prior Art
The currently fielded Army aviation goggles are the AN/AVS-6 ("ANVIS"), and the AN/PVS-5. They both feature a 40.degree. field of view and low light level image intensification. The intensification is accomplished by employing an objective lens that focuses the outside scenery onto a photocathode tube. The tube then converts the photons to electrons and multiplies the electrons thousands of times. The electrons then strike the rear of the output eyepiece of the tube, where a luminescent phosphor converts the electrons back into photons as an intensified image. A typical phosphor is the green colored P43. The eyepiece lenses focus backwards onto the phosphor screen with the same net focal length as the objective lenses, thereby projecting the image back out to its true location in real space. This provides the user with an intensified, albeit monochromatic, view of the real world.
Head-mounted night vision goggle technology that is currently fielded involves the mounting of the AN/AVS-6 or AN/PVS-5 image intensification goggles on the helmet so they hang directly in front of the user's eyes. This arrangement adds a weight (1.0 pound system weight) and center of gravity moment upon the head that exceeds the U.S. Army Aeromedical Research Lab's recommended crash safety specifications for U.S. Army helicopter pilots. When the intensifier objectives and tubes are arranged at a position back and closer to the ears there is a reduction of the center of gravity moment, but it also increases the left-right separation beyond the normal separation of the human eyes. When the sensor apertures are farther apart than the human eyes, the user perceives an exaggerated sensation of depth perception known as "hyperstereopsis". This condition is proven to be detrimental to helicopter pilot performance when close maneuvering is required.
While the prior art has reported using helmet mounted night vision enhancement devices, none have established a basis for a specific apparatus that is dedicated to the task of resolving the particular problem at hand. What is needed in this instance is a new image intensifier arrangement for a helmet-mounted night vision enhancement system that allows for further correction for center-of-gravity imbalance, and no hyperstereopsis.